New Cam chain tensioner a must?

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Got a 07 yz250f I've been rebuilding new cases, bearings, crank, seals ect. The bike is pretty much all new bottom and top. Should I replace the cam tensioner as well? The guy I bought it off of said he had just replaced it and the chain a few rides before the chain slaped the cases and exploded them lol. I did buy a new cam chain alrdy but the tensioner still looks new. What makes these fail? I've read the horror of low idle disaster and poof 1200 bucks down the drain after just replacing you head, valves, piston ect. Are the manual tensioners more reliable? I have the stock one on ATM but kinda wanted to see everyone's thoughts before I finish the rebuild.

Edited April 21, 2016 by msizemore79

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I would not get a manual tensioner. The OEM tensioner is pretty reliable and only a few things can go wrong with it. The spring can get weak or become detached. The internals can wear and slip under load. Or it can get dirty. The guides wear out also.

I think there are checks called out in the manual. Make sure the spring unwinds firmly. You should not be able to push the plunger in without rotating the winder. And it should wind up and unwind smoothly.

I take it the drive chain is what hit the case? If it was the cam chain I would replace the tensioner, but I’d suspect the guides to be more the culprit.